Tor has guidelines that define a set of rules/techniques to assure anonymity. Some examples are browsing in small window mode so your screen resolution can't be detected, using HTTPS everywhere, and never using third-party plugins and blocking parts of Javascript. Since Tor encrypts data, let's assume that someone uses it to be a repeat-offender (harassment, bullying, DDOS/DOS attacks/etc.), is it possible that said person could possibly be impossible to track among any means possible, even given their annoying, disruptive and destructive nature? I mean nothing that would cause a major red flag (terrorism, etc.), but that can otherwise delay, impede and ruin/torment others through anonymity?
I ask because I've heard of some online communities that say they have no options but to deal with repeat-offending trolls no matter what, and the site cannot stop them because of Tor/proxies/VPN/etc., and they are deliberating harassing, impeding and otherwise being destructive and toxic to communities.
Is it true that, given some habitual measures of abuse, you can sometimes be truly anonymous?